The Stovebolt Site Forums The Shop Area Driveline 47 3100, 4 speed trans on floor -educate me!

Hi all,

Newbie trying to make sense of things here. My truck is a 1947 3100, it has the original 216, had a 4 speed on the floor with super low first, which is now gone, and a torque tube rear end. I am aiming for originality and want to use the original set up. Can anyone tell me what years etc used this transmission? Anyone near SF Bay Area have one for sale? Thanks!

1947 was a transition year. The early series used a sliding gear that had been used since about 1940 and the late series may have used a SM420 that was used for about 20 years. Most of the 1947 models used the old sliding gear transmission. Books cite the SM420 as being offered in late 1947, but all I have ever seen is the sliding gear type. There is a difference in the bolt pattern in the two transmissions.

So a transmission from early 47 or before (until about 1940) will work but later will not due to a bolt pattern change?

Any other route I can go?

Again, this is a 1947 3100 AD truck with the stock 216 and torque tube rear end.

Matt,

The truck/commercial clutch housing is the same within each of these sets of years: from 38-47 and from 48-53 and from 54-??

If you want to stay with your original-style transmission, it was the same from 41-47.

If you want to go with a 1948 or later transmission, you will need people to tell you about using a newer clutch housing with your engine (should be OK) and tell you about any tricks with motor mounts and enclosed driveshaft attachments.

If you want originality then fix your trans. I have a lot of NOS gears and shafts for them. These are simple units. E-mail me if you want. bwbugay@aol.com

ChevyB -I wish I could rebuild the trans but unfortunately I can't because my dad threw it away before moving across country because a shop told him it was junk when he took it in to be rebuilt!

I have no problem going to a later, similar transmission -perhaps the 48 - 54 variety, so long as I can still use the engine and rear end, and it's a 4 on the floor.

Sounds like to do this I need a 48 - 54 transmission and bellhousing. Anything else I might need?

The SM420 of the 48-54 variety is 2" longer then the original sliding gear crash box, so you need to figure out what to do with the extra 2" of torque tube.

matt in oakland, a picture of the face of the bellhousing will tell if indeed the truck had a sm420 or the earlier crash box. You can email a pic to bigbadswingdaddy@yahoo.com, and I could tell you what was in there. I'm just across the bay from you.

John

Donf -is the torque tube from the later drivelines shorter too? I know of one by my house I can buy out of a '50 I think.

John -when I see it again I'll take a picture and send it to you.

All -can a column shift box be converted to floor shift?

More dumb questions to follow -stay tuned!

Donf:

"The SM420 of the 48-54 variety is 2" longer then the original sliding gear crash box, so you need to figure out what to do with the extra 2" of torque tube."

Shortening the driveshaft and torque tube is not a problem. I just did that in my home shop when I used a '37 Chevy car rear axle in my '36 Chevy pickup in order to be able to use 3.55 gears from a '50-54 powerglide equipped Chevy car.

Also, it's been my experience that complete excellent used transmissions can often be found on ebay and craigslist for less than the cost of a single part from a professional vendor, often for MUCH less. For example, I recently bought a complete '36 Chevy synchromesh transmission in apparently excellent condition on ebay for $36 and I was the ONLY bidder. Those parts are scrap iron to street rod builders.

59Sprint: Not certain about the length of different torque tubes, just know there are many different lengths. Go to tech tips, look for 'Old Online Chevy Manuals' http://chevy.oldcarmanualproject.com/chevyresto/index.htm
Early parts book will have length of different propeller shafts.

Yar: Would be interested in how you shortened torque tube and propeller shaft. I looked at one with just that intention but passed on the idea as more then I wanted to take on.

"Yar: Would be interested in how you shortened torque tube and propeller shaft. I looked at one with just that intention but passed on the idea as more then I wanted to take on."

Hi Donf. To shorten the torque tube I cut out a piece at the front in the full diameter section and welded it back together using a 7018 electrode running electrode positive. I made a very basic but effective jig to hold it in alignment. If you are interested I think I still have a picture of the jig. I don't know how to post pictures here but I could email you the picture if you give me your email address. Mine is rwaldbaum@aol.com.

To shorten the driveshaft I chopped off the back of the driveshaft then machined out the weld that holds the female socket into the back driveshaft stub. Because I was using a 3.55 gear set from a '51 Chevy car, I had to reduce the OD of the '51 female socket to the correct size to fit into the '37 driveshaft. Then I welded it in with the same stick welding setup.

I hope some people will read this and see how simple these modifications are. This stuff may sound scary but it is not rocket science or I wouldn't be able to do it. It is completely unnecessary to farm these projects out to expensive machione shops or avoid them completely. There is always a friend or neighbor willing to help.

Yar,

Thanks for sharing your torque tube shortening technique. A simple and elegant approach that provides many additional options.

Thank you, Ray.